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accomplished by other means. With the registration of pesticides, large-scale field
studies are occasionally carried out to resolve questions that turn up in normal risk
assessment (Somerville and Walker 1990) but are far too expensive and time con-
suming to be used with any regularity. Lack of control of variables and the difficulty
of achieving adequate replication are fundamental problems. However, the develop-
ment of new strategies, and the development of new biomarker assays could pave the
way for more informative and cost-effective investigations of the effects of pollutants
in the field. Small-scale field studies and semi-field studies are used for risk assess-
ment of pesticides to bees (Thompson and Maus 2007).
That said, long-term case studies of pollution by chemicals can give important
insights into problems with other similar chemicals that may arise later on. Cases
in point include long-term studies that have been carried out on persistent lipophilic
compounds such as OC insecticides, PCBs, organomercury compounds, and organo-
tin compounds, which have been described in this second section of this topic. With
the advance of science, results from well-conducted field studies can be looked at
retrospectively to gain new insights—with the benefit of hindsight. In the final analy-
sis, the natural environment is too complex to just make simple predictions with
laboratory-based models, and there is no adequate substitute for hard data from the
real world. It is important that long term in-depth studies of pollution of the natural
environment continue.
The use of biotic indices in environmental monitoring is one way of identifying
existing/developing pollution problems in the field (see Chapter 11 in Walker et al.
2000). Such ecological profiling can flag up structural changes in communities that
may be the consequence of pollution. For example, the RIVPACS system can iden-
tify changes in the macroinvertebrate communities of freshwater systems (Wright
1995). It is important that adverse changes found during biomonitoring are followed
up by the use of biomarker assays (indicator organisms or bioassays or both) and
chemical analysis to identify the cause. As noted earlier, improvements in biomarker
technology should make this task easier and cheaper to perform.
Biomarker assays can be used to establish the relationship between the levels of
chemicals present and consequent biological effects both in controlled field studies
(e.g., field trials with pesticides) and in the investigation of the biological conse-
quences of existing or developing pollution problems in the field. In the latter case,
clean organisms can be deployed to both clean and polluted sites in the field, and
biomarker responses measured in them. Organisms can be deployed along pollu-
tion gradients so that dose-response curves can be obtained for the field for com-
parison with those obtained in the laboratory. An example of this approach was the
deployment of
Mytilus edulis
along PAH gradients in the marine environment and
the measurement of scope for growth (Chapter 9, Section 9.6). The challenge here
is to take the further step and relate biomarker responses to population parameters
so that predictions of population effects can be made using mathematical models.
The predictions from the models can then be compared with the actual state of the
populations in the field. The validation of such an approach should lead to its wider
employment in the general field of environmental risk assessment.
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